A synopsis of Kuhn's classic "The Structure of Scientific Revolutions" and a rebuttal (long, but well worth it, IMHO)

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Here's a synopsis of a classic in the philosophy of science: Kuhn's "The Structure of Scientific Revolutions."

In essence, Kuhn argued that improvements in science doesn't bring us any closer to the truth; they're just "paradigm shifts." (btw, he's the one who coined the term "paradigm")

(In my next post I'll put up a rebuttal by Prof. Steven Weinberg)

from The Structure of Scientific Revolutions

The Structure of Scientific Revolutions

by Thomas S. Kuhn

A Synopsis from the orginal by Professor Frank Pajares

I Introduction

A scientific community cannot practice its trade without some set of received beliefs. These beliefs form the foundation of the "educational initiation that prepares and licenses the student for professional practice". The nature of the "rigorous and rigid" preparation helps ensure that the received beliefs are firmly fixed in the student's mind. Scientists take great pains to defend the assumption that scientists know what the world is like...To this end, "normal science" will often suppress novelties which undermine its foundations. Research is therefore not about discovering the unknown, but rather "a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education".

A shift in professional commitments to shared assumptions takes place when an anomaly undermines the basic tenets of the current scientific practice These shifts are what Kuhn describes as scientific revolutions - "the tradition-shattering complements to the tradition-bound activity of normal science" New assumptions "paradigms" - require the reconstruction of prior assumptions and the re-evaluation of prior facts. This is difficult and time consuming. It is also strongly resisted by the established community.

II The Route to Normal Science

So how are paradigms created and what do they contribute to scientific inquiry?

Normal science "means research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice". These achievements must be sufficiently unprecedented to attract an enduring group of adherents away from competing modes of scientific activity and sufficiently open-ended to leave all sorts of problems for the redefined group of practitioners (and their students) to resolve. These achievements can be called paradigms. Students study these paradigms in order to become members of the particular scientific community in which they will later practice.

Because the student largely learns from and is mentored by researchers "who learned the bases of their field from the same concrete models" there is seldom disagreement over fundamentals. Men whose research is based on shared paradigms are committed to the same rules and standards for scientific practice. A shared commitment to a paradigm ensures that its practitioners engage in the paradigmatic observations that its own paradigm can do most to explain. Paradigms help scientific communities to bound their discipline in that they help the scientist to create avenues of inquiry, formulate questions, select methods with which to examine questions, define areas of relevance. and establish or create meaning. A paradigm is essential to scientific inquiry - "no natural history can be interpreted in the absence of at least some implicit body of intertwined theoretical and methodological belief that permits selection, evaluation, and criticism".

How are paradigms created, and how do scientific revolutions take place? Inquiry begins with a random collection of "mere facts" (although, often, a body of beliefs is already implicit in the collection). During these early stages of inquiry, different researchers confronting the same phenomena describe and interpret them in different ways. In time, these descriptions and interpretations entirely disappear. A pre-paradigmatic school appears. Such a school often emphasises a special part of the collection of facts. Often, these schools vie for pre-eminence. From the competition of these pre-paradigmatic schools, one paradigm emerges - "To be accepted as a paradigm, a theory must seem better than its competitors, but it need not, and in fact never does, explain all the facts with which it can be confronted", thus making research possible. As a paradigm grows in strength and in the number of advocates, the other pre-paradigmatic schools or the previous paradigm fade.

A paradigm transforms a group into a profession or, at least, a discipline. And from this follow the formation of specialised journals, foundation of professional bodies and a claim to a special place in academe. There is a promulgation of scholarly articles intended for and "addressed only to professional colleagues, [those] whose knowledge of a shared paradigm can be assumed and who prove to be the only ones able to read the papers addressed to them".

III - The Nature of Normal Science.

If a paradigm consists of basic and incontrovertible assumptions about the nature of the discipline, what questions are left to ask? When they first appear, paradigms are limited in scope and in precision. But more successful does not mean completely successful with a single problem or notably successful with any large number. Initially, a paradigm offers the promise of success. Normal science consists in the actualisation of that promise. This is achieved by extending the knowledge of those facts that the paradigm displays as particularly revealing, increasing the extent of the match between those facts and the paradigm's predictions, and further articulation of the paradigm itself.

In other words, there is a good deal of mopping-up to be done. Mop-up operations are what engage most scientists throughout their careers. Mopping-up is what normal science is all about! This paradigm-based research is "an attempt to force nature into the pre-formed and relatively inflexible box that the paradigm supplies". No effort is made to call forth new sorts of phenomena, no effort to discover anomalies. When anomalies pop up, they are usually discarded or ignored. Anomalies are usually not even noticed and no effort is made to invent a new theory (and theres no tolerance for those who try). Those restrictions, born from confidence in a paradigm, turn out to be essential to the development of science. By focusing attention on a small range of relatively esoteric problems, the paradigm forces scientists to investigate some part of nature in a detail and depth that would otherwise be unimaginable" and, when the paradigm ceases to function properly, scientists begin to behave differently and the nature of their research problems changes.

IV - Normal Science as Puzzle-solving.

Doing research is essentially like solving a puzzle. Puzzles have rules. Puzzles generally have predetermined solutions.

A striking feature of doing research is that the aim is to discover what is known in advance. This in spite of the fact that the range of anticipated results is small compared to the possible results. When the outcome of a research project does not fall into this anticipated result range, it is generally considered a failure.

So why do research? Results add to the scope and precision with which a paradigm can be applied. The way to obtain the results usually remains very much in doubt - this is the challenge of the puzzle. Solving the puzzle can be fun, and expert puzzle-solvers make a very nice living. To classify as a puzzle (as a genuine research question), a problem must be characterised by more than the assured solution, but at the same time solutions should be consistent with paradigmatic assumptions.

Despite the fact that novelty is not sought and that accepted belief is generally not challenged, the scientific enterprise can and does bring about unexpected results.

V - The Priority of Paradigms.

The paradigms of a mature scientific community can be determined with relative ease. The "rules" used by scientists who share a paradigm are not so easily determined. Some reasons for this are that scientists can disagree on the interpretation of a paradigm. The existence of a paradigm need not imply that any full set of rules exist. Also, scientists are often guided by tacit knowledge - knowledge acquired through practice and that cannot be articulated explicitly. Further, the attributes shared by a paradigm are not always readily apparent.

Paradigms can determine normal science without the intervention of discoverable rules or shared assumptions. In part, this is because it is very difficult to discover the rules that guide particular normal-science traditions. Scientists never learn concepts, laws, and theories in the abstract and by themselves. They generally learn these with and through their applications. New theory is taught in tandem with its application to a concrete range of phenomena.

Sub-specialties are differently educated and focus on different applications for their research findings. A paradigm can determine several traditions of normal science that overlap without being coextensive. Consequently, changes in a paradigm affect different sub-specialties differently. "A revolution produced within one of these traditions will not necessarily extend to the others as well".

When scientists disagree about whether the fundamental problems of their field have been solved, the search for rules gains a function that it does not ordinarily possess .

VI - Anomaly and the Emergence of Scientific Discoveries.

If normal science is so rigid and if scientific communities are so close-knit, how can a paradigm change take place? Paradigm changes can result from discovery brought about by encounters with anomaly. Normal science does not aim at novelties of fact or theory and, when successful, finds none. Nonetheless, new and unsuspected phenomena are repeatedly uncovered by scientific research, and radical new theories have again and again been invented by scientists .

Fundamental novelties of fact and theory bring about paradigm change. So how does paradigm change come about? There are two ways: through discovery - novelty of fact - or by invention  novelty of theory. Discovery begins with the awareness of anomaly - the recognition that nature has violated the paradigm-induced expectations that govern normal science. The area of the anomaly is then explored. The paradigm change is complete when the paradigm has been adjusted so that the anomalous become the expected. The result is that the scientist is able "to see nature in a different way".. How paradigms change as a result of invention is discussed in greater detail in the following chapter.

Although normal science is a pursuit not directed to novelties and tending at first to suppress them, it is nonetheless very effective in causing them to arise. Why? An initial paradigm accounts quite successfully for most of the observations and experiments readily accessible to that science's practitioners. Research results in the construction of elaborate equipment, development of an esoteric and shared vocabulary, refinement of concepts that increasingly lessens their resemblance to their usual common-sense prototypes. This professionalisation leads to immense restriction of the scientist's vision, rigid science, resistance to paradigm change, and a detail of information and precision of the observation-theory match that can be achieved in no other way. New and refined methods and instruments result in greater precision and understanding of the paradigm. Only when researchers know with precision what to expect from an experiment can they recognise that something has gone wrong. Consequently, anomaly appears only against the background provided by the paradigm . The more precise and far-reaching the paradigm, the more sensitive it is to detecting an anomaly and inducing change. By resisting change, a paradigm guarantees that anomalies that lead to paradigm change will penetrate existing knowledge to the core. VII - Crisis and the Emergence of Scientific Theories.

As is the case with discovery, a change in an existing theory that results in the invention of a new theory is also brought about by the awareness of anomaly. The emergence of a new theory is generated by the persistent failure of the puzzles of normal science to be solved as they should. Failure of existing rules is the prelude to a search for new ones . These failures can be brought about by observed discrepancies between theory and fact or changes in social/cultural climates Such failures are generally long recognised, which is why crises are seldom surprising. Neither problems nor puzzles yield often to the first attack . Recall that paradigm and theory resist change and are extremely resilient. Philosophers of science have repeatedly demonstrated that more than one theoretical construction can always be placed upon a given collection of data . In early stages of a paradigm, such theoretical alternatives are easily invented. Once a paradigm is entrenched (and the tools of the paradigm prove useful to solve the problems the paradigm defines), theoretical alternatives are strongly resisted. As in manufacture so in science--retooling is an extravagance to be reserved for the occasion that demands it . Crises provide the opportunity to retool.

VIII - The Response to Crisis.

The awareness and acknowledgement that a crisis exists loosens theoretical stereotypes and provides the incremental data necessary for a fundamental paradigm shift. Normal science does and must continually strive to bring theory and fact into closer agreement. The recognition and acknowledgement of anomalies result in crises that are a necessary precondition for the emergence of novel theories and for paradigm change. Crisis is the essential tension implicit in scientific research. There is no such thing as research without counterinstances. These counterinstances create tension and crisis. Crisis is always implicit in research because every problem that normal science sees as a puzzle can be seen, from another viewpoint, as a counterinstance and thus as a source of crisis .

In responding to these crises, scientists generally do not renounce the paradigm that has led them into crisis. Rather, they usually devise numerous articulations and ad hoc modifications of their theory in order to eliminate any apparent conflict. Some, unable to tolerate the crisis, leave the profession. As a rule, persistent and recognised anomaly does not induce crisis . Failure to achieve the expected solution to a puzzle discredits only the scientist and not the theory To evoke a crisis, an anomaly must usually be more than just an anomaly. Scientists who paused and examined every anomaly would not get much accomplished. An anomaly must come to be seen as more than just another puzzle of normal science.

All crises begin with the blurring of a paradigm and the consequent loosening of the rules for normal research. As this process develops, the anomaly comes to be more generally recognised as such, more attention is devoted to it by more of the field's eminent authorities. The field begins to look quite different: scientists express explicit discontent, competing articulations of the paradigm proliferate and scholars view a resolution as the subject matter of their discipline. To this end, they first isolate the anomaly more precisely and give it structure. They push the rules of normal science harder than ever to see, in the area of difficulty, just where and how far they can be made to work.

All crises close in one of three ways. (i) Normal science proves able to handle the crisis-provoking problem and all returns to "normal." (ii) The problem resists and is labelled, but it is perceived as resulting from the field's failure to possess the necessary tools with which to solve it, and so scientists set it aside for a future generation with more developed tools. (iii) A new candidate for paradigm emerges, and a battle over its acceptance ensues. Once it has achieved the status of paradigm, a paradigm is declared invalid only if an alternate candidate is available to take its place . Because there is no such thing as research in the absence of a paradigm, to reject one paradigm without simultaneously substituting another is to reject science itself. To declare a paradigm invalid will require more than the falsification of the paradigm by direct comparison with nature. The judgement leading to this decision involves the comparison of the existing paradigm with nature and with the alternate candidate. Transition from a paradigm in crisis to a new one from which a new tradition of normal science can emerge is not a cumulative process. It is a reconstruction of the field from new fundamentals. This reconstruction changes some of the field's foundational theoretical generalisations. It changes methods and applications. It alters the rules.

How do new paradigms finally emerge? Some emerge all at once, sometimes in the middle of the night, in the mind of a man deeply immersed in crisis. Those who achieve fundamental inventions of a new paradigm have generally been either very young or very new to the field whose paradigm they changed. Much of this process is inscrutable and may be permanently so.

IX - The Nature and Necessity of Scientific Revolutions.

Why should a paradigm change be called a revolution? What are the functions of scientific revolutions in the development of science? A scientific revolution is a non-cumulative developmental episode in which an older paradigm is replaced in whole or in part by an incompatible new one . A scientific revolution that results in paradigm change is analogous to a political revolution. Political revolutions begin with a growing sense by members of the community that existing institutions have ceased adequately to meet the problems posed by an environment that they have in part created. The dissatisfaction with existing institutions is generally restricted to a segment of the political community. Political revolutions aim to change political institutions in ways that those institutions themselves prohibit. As crisis deepens, individuals commit themselves to some concrete proposal for the reconstruction of society in a new institutional framework. Competing camps and parties form. One camp seeks to defend the old institutional constellation. One (or more) camps seek to institute a new political order. As polarisation occurs, political recourse fails. Parties to a revolutionary conflict finally resort to the techniques of mass persuasion.

Like the choice between competing political institutions, that between competing paradigms proves to be a choice between fundamentally incompatible modes of community life. Paradigmatic differences cannot be reconciled. When paradigms enter into a debate about fundamental questions and paradigm choice, each group uses its own paradigm to argue in that paradigm's defence The result is a circularity and inability to share a universe of discourse. A successful new paradigm permits predictions that are different from those derived from its predecessor . That difference could not occur if the two were logically compatible. In the process of being assimilated, the second must displace the first.

Consequently, the assimilation of either a new sort of phenomenon or a new scientific theory must demand the rejection of an older paradigm . If this were not so, scientific development would be genuinely cumulative. Normal research is cumulative, but not scientific revolution. New paradigms arise with destructive changes in beliefs about nature.

Consequently, "the normal-scientific tradition that emerges from a scientific revolution is not only incompatible but often actually incommensurable with that which has gone before". In the circular argument that results from this conversation, each paradigm will satisfy more or less the criteria that it dictates for itself, and fall short of a few of those dictated by its opponent. Since no two paradigms leave all the same problems unsolved, paradigm debates always involve the question: Which problems is it more significant to have solved? In the final analysis, this involves a question of values that lie outside of normal science altogether. It is this recourse to external criteria that most obviously makes paradigm debates revolutionary.

X - Revolutions as Changes of World View.

During scientific revolutions, scientists see new and different things when looking with familiar instruments in places they have looked before. Familiar objects are seen in a different light and joined by unfamiliar ones as well. Scientists see new things when looking at old objects. In a sense, after a revolution, scientists are responding to a different world.

Why does a shift in view occur? Genius? Flashes of intuition? Sure. Because different scientists interpret their observations differently? No. Observations are themselves nearly always different. Observations are conducted within a paradigmatic framework, so the interpretative enterprise can only articulate a paradigm, not correct it. Because of factors embedded in the nature of human perception and retinal impression? No doubt, but our knowledge is simply not yet advanced enough on this matter. Changes in definitional conventions? No. Because the existing paradigm fails to fit? Always. Because of a change in the relation between the scientist's manipulations and the paradigm or between the manipulations and their concrete results? You bet. It is hard to make nature fit a paradigm.

XI - The Invisibility of Revolutions.

Because paradigm shifts are generally viewed not as revolutions but as additions to scientific knowledge, and because the history of the field is represented in the new textbooks that accompany a new paradigm, a scientific revolution seems invisible.

The image of creative scientific activity is largely created by a field's textbooks. Textbooks are the pedagogic vehicles for the perpetuation of normal science. These texts become the authoritative source of the history of science. Both the layman's and the practitioner's knowledge of science is based on textbooks. A field's texts must be rewritten in the aftermath of a scientific revolution. Once rewritten, they inevitably disguise not only the role but the existence and significance of the revolutions that produced them. The resulting textbooks truncate the scientist's sense of his discipline's history and supply a substitute for what they eliminate. More often than not, they contain very little history at all. In the rewrite, earlier scientists are represented as having worked on the same set of fixed problems and in accordance with the same set of fixed canons that the most recent revolution and method has made seem scientific. Why dignify what science's best and most persistent efforts have made it possible to discard?

The historical reconstruction of previous paradigms and theorists in scientific textbooks make the history of science look linear or cumulative, a tendency that even affects scientists looking back at their own research . These misconstructions render revolutions invisible. They also work to deny revolutions as a function. Science textbooks present the inaccurate view that science has reached its present state by a series of individual discoveries and inventions that, when gathered together, constitute the modern body of technical knowledge - the addition of bricks to a building. This piecemeal-discovered facts approach of a textbook presentation illustrates the pattern of historical mistakes that misleads both students and laymen about the nature of the scientific enterprise. More than any other single aspect of science, the textbook has determined our image of the nature of science and of the role of discovery and invention in its advance.

XII - The Resolution of Revolutions.

How do the proponents of a competing paradigm convert the entire profession or the relevant subgroup to their way of seeing science and the world? What causes a group to abandon one tradition of normal research in favour of another?

Scientific revolutions come about when one paradigm displaces another after a period of paradigm-testing that occurs only after persistent failure to solve a noteworthy puzzle has given rise to crisis. This process is analogous to natural selection: one theory becomes the most viable among the actual alternatives in a particular historical situation.

What is the process by which a new candidate for paradigm replaces its predecessor? At the start, a new candidate for paradigm may have few supporters (and the motives of the supporters may be suspect). If the supporters are competent, they will improve the paradigm, explore its possibilities, and show what it would be like to belong to the community guided by it. For the paradigm destined to win, the number and strength of the persuasive arguments in its favour will increase. As more and more scientists are converted, exploration increases. The number of experiments, instruments, articles, and books based on the paradigm will multiply. More scientists, convinced of the new view's fruitfulness, will adopt the new mode of practising normal science, until only a few elderly hold-outs remain. And we cannot say that they are (or were) wrong. Perhaps the scientist who continues to resist after the whole profession has been converted has ipso facto ceased to be a scientist.

XIII - Progress Through Revolutions.

In the face of the arguments previously made, why does science progress, how does it progress, and what is the nature of its progress?

To a very great extent, the term science is reserved for fields that do progress in obvious ways. But does a field make progress because it is a science, or is it a science because it makes progress? Normal science progresses because the enterprise shares certain salient characteristics, Members of a mature scientific community work from a single paradigm or from a closely related set. Very rarely do different scientific communities investigate the same problems. The result of successful creative work is progress.

Even if we argue that a field does not make progress, that does not mean that an individual school or discipline within that field does not. The man who argues that philosophy has made no progress emphasises that there are still Aristotelians, not that Aristotelianism has failed to progress. It is only during periods of normal science that progress seems both obvious and assured. In part, this progress is in the eye of the beholder. The absence of competing paradigms that question each other's aims and standards makes the progress of a normal-scientific community far easier to see. The acceptance of a paradigm frees the community from the need to constantly re-examine its first principles and foundational assumptions. Members of the community can concentrate on the subtlest and most esoteric of the phenomena that concern it. Because scientists work only for an audience of colleagues, an audience that shares values and beliefs, a single set of standards can be taken for granted. Unlike in other disciplines, the scientist need not select problems because they urgently need solution and without regard for the tools available to solve them. The social scientists tend to defend their choice of a research problem chiefly in terms of the social importance of achieving a solution. Which group would one then expect to solve problems at a more rapid rate?

We may have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth . The developmental process described by Kuhn is a process of evolution from primitive beginnings. It is a process whose successive stages are characterised by an increasingly detailed and refined understanding of nature. This is not a process of evolution toward anything. Important questions arise. Must there be a goal set by nature in advance? Does it really help to imagine that there is some one full, objective, true account of nature? Is the proper measure of scientific achievement the extent to which it brings us closer to an ultimate goal? The analogy that relates the evolution of organisms to the evolution of scientific ideas "is nearly perfect" . The resolution of revolutions is the selection by conflict within the scientific community of the fittest way to practice future science. The net result of a sequence of such revolutionary selections, separated by period of normal research, is the wonderfully adapted set of instruments we call modern scientific knowledge. Successive stages in that developmental process are marked by an increase in articulation and specialisation. The process occurs without benefit of a set goal and without benefit of any permanent fixed scientific truth. What must the world be like in order than man may know it?

This synopsis is an edited version of an outline prepared by Professor Frank Pajares, Emory University.

-- eve (eve_rebekah@yahoo.com), July 21, 2000


And, a well-known rebuttal...

Steven Weinberg on scientific revolutions

These are excerpts from an article by Steven Weinberg published in the New York Review of Books, Vol XLV, Number 15 (1998).

from Rebuttal< /a>

by Professor Steven Weinberg; Department of Physics; University of Texas at Austin

I first read Thomas Kuhn's famous book The Structure of Scientific Revolutions a quarter-century ago, soon after the publication of the second edition. I had known Kuhn only slightly when we had been together on the faculty at Berkeley in the early 1960s, but I came to like and admire him later, when he came to MIT. His book I found exciting.

Evidently others felt the same. Structure has had a wider influence than any other book on the history of science.

... Structure describes the history of science as a cyclic process. There are periods of "normal science" characterized by what Kuhn sometimes called a "paradigm" and sometimes called a "common disciplinary matrix." Whatever you call it, it describes a consensus view: in the period of normal science, scientists tend to agree about what phenomena are relevant and what constitutes an explanation of these phenomena, about what problems are worth solving and what is a solution of a problem. Near the end of a period of normal science a crisis occurs--experiments give results that don't fit existing theories, or internal contradictions are discovered in these theories. There is alarm and confusion. Strange ideas fill the scientific literature. Eventually there is a revolution. Scientists become converted to a new way of looking at nature, resulting eventually in a new period of normal science. The "paradigm" has shifted.

To give an example given special attention in Structure, after the wide-spread acceptance of Newton's physical theories--the Newtonian paradigm--in the eighteenth century, there began a period of normal science in the study of motion and gravitation. Scientists used Newtonian theory to make increasingly accurate calculations of planetary orbits, leading to spectacular successes like the prediction in 1846 of the existence and orbit of the planet Neptune before astronomers discovered it. By the end of the nineteenth century there was a crisis: a failure to understand the motion of light. The problem was solved through a paradigm shift, a revolutionary revision in the understanding of space and time carried out by Einstein in the decade between 1905 and 1915. Motion affects the flow of time; matter and energy can be converted into each other; and gravitation is a curvature in space-time. Einstein's theory of relativity then became the new paradigm, and the study of motion and gravitation entered upon a new period of normal science.

Though one can question the extent to which Kuhn's cyclic theory of scientific revolution fits what we know of the history of science, in itself this theory would not be very disturbing, nor would it have made Kuhn's book famous. For many people, it is Kuhn's reinvention of the word "paradigm" that has been either most useful or most objectionable.

... But the quarrel over the word "paradigm" seems to me unimportant. Kuhn was right that there is more to a scientific consensus than just a set of explicit theories. We need a word for the complex of attitudes and traditions that go along with our theories in a period of normal science, and "paradigm" will do as well as any other. What does bother me on rereading Structure and some of Kuhn's later writings is his radically sceptical conclusions about what is accomplished in the work of science. And it is just these conclusions that have made Kuhn a hero to the philosophers, historians, sociologists, and cultural critics who question the objective character of scientific knowledge, and who prefer to describe scientific theories as social constructions, not so different from democracy or baseball.

Kuhn made the shift from one paradigm to another seem more like a religious conversion than an exercise of reason. He argued that our theories change so much in a paradigm shift that it is nearly impossible for scientists after a scientific revolution to see things as they had been seen under the previous paradigm. Kuhn compared the shift from one paradigm to another to a gestalt flip, like the optical illusion created by pictures in which what had seemed to be white rabbits against a black background suddenly appear as black goats against a white background. But for Kuhn the shift is more profound; he added that "the scientist does not preserve the gestalt subject's freedom to switch back and forth between ways of seeing." Kuhn argued further that in scientific revolutions it is not only our scientific theories that change but the very standards by which scientific theories are judged, so that the paradigms that govern successive periods of normal science are incommensurable. He went on to reason that since a paradigm shift means complete abandonment of an earlier paradigm, and there is no common standard to judge scientific theories developed under different paradigms, there can be no sense in which theories developed after a scientific revolution can be said to add cumulatively to what was known before the revolution. Only within the context of a paradigm can we speak of one theory being true or false. Kuhn in Structure concluded, tentatively, "We may, to be more precise, have to relinquish the notion explicit or implicit that changes of paradigm carry scientists and those who learn from them closer and closer to the truth." More recently, in his Rothschild Lecture at Harvard in 1992, Kuhn remarked that it is hard to imagine what can be meant by the phrase that a scientific theory takes us "closer to the truth."

Kuhn did not deny that there is progress in science, but he denied that it is progress toward anything. He often used the metaphor of biological evolution: scientific progress for him was like evolution as described by Darwin, a process driven from behind, rather than pulled toward some fixed goal to which it grows ever closer. For him, the natural selection of scientific theories is driven by problem solving. When during a period of normal science, it turns out that some problems can't be solved using existing theories, then new ideas proliferate, and the ideas that survive are those that do best at solving these problems. But according to Kuhn, just as there was nothing inevitable about mammals appearing in the Cretaceous period and out-surviving the dinosaurs when a comet hit the earth, so also there is nothing built into nature that made it inevitable that our science would evolve in the direction of Maxwell's equation or general relativity. Kuhn recognizes that Maxwell's and Einstein's theories are better than those that preceded them, in the same way that mammals turned out to be better than dinosaurs at surviving the effects of comet impacts, but when new problems arise they will be replaced by new theories that are better at solving those problems, and so on, with no overall improvement.

All this is wormwood to scientists like myself, who think the task of science is to bring us closer and closer to objective truth. But Kuhn's conclusions are delicious to those who take a more skeptical view of the pretentions of science. If scientific theories can only be judged within the context of a particular paradigm, then in this respect the scientific theories of any one paradigm are not privileged over other ways of looking at the world, such as shamanism or astrolgy or creationism. If the transition from one paradigm to another cannot be judged by any external standard, then perhaps it is culture rather than nature that dictates the content of scientific theories.

Kuhn himself was not always happy with those who invoked his work. In 1965 he complained that for the philosopher Paul Feyerabend to describe his arguments as a defense of irrationality in science seemed to him to be "not only absurd but vaguely obscene"... But even when we put aside the excesses of Kuhn's admirers, the radical part of Kuhn's theory of scientific revolutions is radical enough. And I think it is quite wrong.

It is not true that scientists are unable to "switch back and forth between ways of seeing," and that after a scientific revolution they become incapable of understanding the science that went before it. One of the paradigm shifts to which Kuhn gives much attention in Structure is the replacement at the beginning of this century of Newtonian mechanics by the relativistic mechanics of Einstein. But in fact in educating new physicists the first thing that we teach them is still good old Newtonian mechanics, and they never forget how to think in Newtonian terms, even after they learn about Einstein's theory of relativity. Kuhn himself as an instructor at Harvard must have taught Newtonian mechanics to undergraduates.

In defending his position, Kuhn argued that the words we use and the symbols in our equations mean different things before and after a scientific revolution; for instance, physicists meant different things by mass before and after the advent of relativity. It is true that there was a good deal of uncertainty about the concept of mass during the Einsteinian revolution. For a while there was talk of "longitudinal" and "transverse" masses, which were supposed to depend on a particle's speed and to resist accelerations along the direction of motion and perpendicular to it. But this has all been resolved. No one today talks of longitudinal or transverse mass, and in fact the term "mass" today is most frequently understood as "rest mass," an intrinsic property of a body that is not changed by motion, which is much the way that mass was understood before Einstein. Meanings can change, but generally they do so in the direction of an increased richness and precision of definition, so that we do not lose the ability to understand the theories of past periods of normal science.

... [S]cientists who come of age in a period of normal science find it extraordinarily difficult to understand the work of scientists in previous scientific revolutions, so that in this respect we are often almost incapable of reliving the "gestalt flip" produced by the revolution. For instance, it is not easy for a physicist today to read Newton's Principia, even in a modern translation from Newton's Latin. The great astrophysicist Subrahmanian Chandrasekhar spent years translating the Principia's reasoning into a form that a modern physicist could understand. But those who participate in a scientific revolution are in a sense living in two worlds: the earlier period of normal science, which is breaking down, and the new period of normal science, which they do not yet fully comprehend. It is much less difficult for scientists in one period of normal science to understand the theories of an earlier paradigm in their mature form.

I was careful earlier to talk about Newtonian mechanics, not Newton's mechanics. In an important sense, especially in his geometric style, Newton is pre-Newtonian. Recall the aphorism of John Maynard Keynes, that Newton was not the first modern scientist but rather the last magician. Newtonianism reached its mature form in the early nineteenth century through the work of Laplace, Lagrange, and others, and it is this mature Newtonianism--which still predates special relativity by a century--that we teach our students today. They have no trouble in understanding it, and they continue to understand it and use it where appropriate after they learn about Einstein's theory of relativity.

Much the same can be said about our understanding of the electrodynamics of James Clerk Maxwell. Maxwell's 1873 Treatise on Electricity and Magnetism is difficult for a modern physicist to read, because it is based on the idea that electric and magnetic fields represent tensions in a physical medium, the ether, in which we no longer believe. In this respect, Maxwell is pre-Maxwellian. (Oliver Heaviside, who helped to refine Maxwell's theory, said of Maxwell that he was only half a Maxwellian.) Maxwellianism--the theory of magnetism, electricity, and light that is based on Maxwell's work--reached its mature form (which does not require reference to an ether) by 1900, and it is this mature Maxwellianism that we teach our students. Later they take courses on quantum mechanics in which they learn that light is composed of particles called photons, and that Maxwell's equations are only approximate; but this does not prevent them from continuing to understand and use Maxwellian electrodynamics where appropriate.

In judging the nature of scientific progress, we have to look at mature scientific theories, not theories at the moments when they are coming into being.

... Nor do scientific revolutions necessarily change the way that we assess our theories, making different paradigms incommensurable. Over the past forty years I have been involved in revolutionary changes in the way that physicists understand the elemntary particles that are the basic constituents of matter. The greater revolutions of this century, quantum mechanics and relativity, were before my time, but they are the basis of the physics research of my generation. Nowhere have I seen any signs of Kuhn's incommensurability between different paradigms. Our ideas have changed, but we have continued to assess our theories in pretty much the same way: a theory is taken as a success if it is based on simple general principles and does a good job of accounting for experimental data in a natural way. I am not saying that we have a book of rules that tells us how to assess theories, or that we have a clear idea of what is meant by "simple general principles" or "natural." I am only saying that whatever we mean, there have been no sudden changes in the way we assess theories, no changes that would make it impossible to compare the truth of theories before and after a revolution.

... It is important to keep straight what does and what does not change in scientific revolutions, a distinction that is not made in Structure. There is a "hard" part of modern physical theories ("hard" meaning not difficult, but durable, like bones in paleontology or potsherds in archeology) that usually consists of the equations themselves, together with some understandings about what the symbols mean operationally and about the sorts of phenomena to which they apply. Then there is a "soft" part; it is the vision of reality that we use to explain to ourselves why the equations work. The soft part does change; we no longer believe in Maxwell's ether, and we know that there is more to nature than Newton's particles and forces. The changes in the soft part of scientific theories also produce changes in our understanding of the conditions under which the hard part is a good approximation. But after our theories reach mature forms, their hard parts represent permanent accomplishments. If you have bought one of those T-shirts with Maxwell's equations on the front, you may have to worry about its going out of style, but not about its becoming false. We will go on teaching Maxwellian electrodynamics as long as there are scientists. I can't see any sense in which the increase in scope and accuracy of the hard parts of our theories is not a cumulative approach to truth.

... Kuhn's view of scientific progress would leave us with a mystery: Why does anyone bother? If one scientific theory is only better than another in its ability to solve the problems that happen to be on our minds today, then why not save ourselves a lot of trouble by putting these problems out of our minds? We don't study elementary particles because they are intrinsically interesting, like people. They are not- -if you have seen one electron, you've seen them all. What drives us onward in the work of science is precisely the sense that there are truths out there to be discovered, truths that once discovered will form a permanent part of human knowledge.

-- eve (
eve_rebekah@yahoo.com), July 21, 2000.

Holy smokes! Although I like the rebuttal, I really didn't underline the whole thing and color it all pink for emphasis!:) (I'm not sure why the link didn't quit; hopefully it's off now.)

-- eve (eve_rebekah@yahoo.com), July 21, 2000.

-- anon (anon@anon.com), July 21, 2000.


Would you repeat the title of that link please?

-- Debra (Thisis@it.com), July 21, 2000.

Aaahhhh. A thread on Kuhn. I will wallow in it. Back later for comment ...

-- Oxy (Oxsys@aol.com), July 21, 2000.

Debra, I certainly will repost the title to the link -- anything for you.

It was:

Rebuttal< /a> by Professor Steven Weinberg; Department of Physics; University of Texas at Austin. I first read Thomas Kuhn's famous book The Structure of Scientific Revolutions a quarter-century ago, soon after...

Now, wait a minute! Time out!! Ok, Debra --- I owe ya one. Good thing I haven't submitted this by mistake -- boy, would that've been embarrassing...now, I'm kinda groggy cuz I haven't had my afternoon coffee yet (yawwwnn)...where's that "back" button (rubs and blinks eyes)........

-- eve (eve_rebekah@yahoo.com), July 21, 2000.

Eve, are you some kinda intellectool or sumpin?

-- (nemesis@awol.com), July 21, 2000.


Honestly, I've never thought of myself in those terms. I just have this incredible, insatiable appetite for understanding life, its challenges and its mysteries.

-- eve (eve_rebekah@yahoo.com), July 21, 2000.

EVE: ROFL, at your last comment, that WILL keep ya busy babe!!!!


-- consumer (shh@aol.com), July 21, 2000.

We will go on teaching Maxwellian electrodynamics as long as there are scientists.

Bzzzzz! How can Prof. Weinburg or anyone else be certain that today's "durable" theory might not be contradicted by tomorrow's evidence, and that person remain "scientific."

The degree that a new theory advances our understanding depends on amount of thought behind it. Hence the effect of that theory's giving birth to a paradigm may or may not bring us closer to objective truth.

-- David L (bumpkin@dnet.net), July 21, 2000.

David L:

I'm not sure how to interpret your comments here. Let me guess...

[Bzzzzz! How can Prof. Weinburg or anyone else be certain that today's "durable" theory might not be contradicted by tomorrow's evidence, and that person remain "scientific."]

He can be certain because that durable theory accurately describes what we can observe and measure, aka reality. He is positing that reality won't change at least with respect to the conditions to which the theory applies. He's careful to make the point that we still both study and use Newtonian mechanics, knowing they break down under extreme conditions. He certainly isn't saying we will never find conditions under which Maxwell's equations might prove limited. Durable, mature theories require extraordinary evidence to modify or extend. It's not unscientific to believe that we actually know some things.

[The degree that a new theory advances our understanding depends on amount of thought behind it.]

And a LOT more. Like evidence, testability, replicability, number and nature of anomalies, etc. A great deal of thought has gone into theories that advanced nothing and sometimes set us back. Our understanding is advanced by *correct* theories, supported by a great deal of rigorous methodology. You can think long and hard about hogwash and get nowhere useful.

-- Flint (flintc@mindspring.com), July 21, 2000.

Buddy, can ya paradigm?

-- (nemesis@awol.com), July 22, 2000.

I agree that as evidence accumulates in support of a theory, the likelihood of that theory being disproven shrinks accordingly. But it never quite shrinks to zero. We expect tomorrow's world to be substantially like today's, but there is no guarantee that some unprecedented event might not overturn principles that had been accepted for a very long time.

We may indeed know some things, but I am not sure how we can know that we know them.

-- David L (bumpkin@dnet.net), July 22, 2000.

[I agree that as evidence accumulates in support of a theory, the likelihood of that theory being disproven shrinks accordingly. But it never quite shrinks to zero.]

I think you're confusing "theory" with the mathematical notion of a "theorem". A theorem can be logically proved within the constraints of a particular set of axioms. A theory is a different beast -- "proving" a theory is a semantic error. A scientific theory is a proposed explanation of some phenomenon. While some theories are discarded entirely, most mature through the process of modification and extension. Over time, the rate of change of a theory diminishes, but never vanishes entirely. We don't believe excellent understanding is arbitrary or meaningless simply because it's never *perfect* understanding.

One tenet of science is that one (imperfect) explanation can be superior to another. It may explain more cases, require less modification to handle exceptions as these exceptions are investigated in more depth, make better predictions, etc. Because superior explanations (theories) are possible, all theories are of course subject to possible improvement.

But saying that because we don't know everything we don't know anything is throwing the baby out with the bathwater. Judging theories in terms of absolutes is the wrong model. Absolutes are for religion, while science deals with the realities of the objective world.

-- Flint (flintc@mindspring.com), July 22, 2000.

I have not read Prof. Weinburg before, so perhaps I am misinterpreting him. But the following does seem to suggest that he wishes to retain the bathwater as well as the baby.

"But after our theories reach mature forms, their hard parts represent permanent accomplishments. If you have bought one of those T-shirts with Maxwell's equations on the front, you may have to worry about its going out of style, but not about its becoming false. We will go on teaching Maxwellian electrodynamics as long as there are scientists."

This goes beyond constructing a useful and highly reliable model consistent with past observations; he seems to be saying that the "hard" parts will persist forever.

-- David L (bumpkin@dnet.net), July 23, 2000.

David L:

Yes, he is saying the hard parts will last so long as physical laws don't change within the range described by those hard parts. In other words, those equations don't become "wrong" should we someday discover that they don't adequately describe observations as, let's say, we approach Planck sizes and energies. They become incomplete, and must be extended rather than rewritten. And over time, the extensions harden as well.

-- Flint (flintc@mindspring.com), July 23, 2000.

Prof. Weinburg may have had in mind the qualification you mention ("so long as physical laws don't change..."), but I can find no trace of it in the above excerpts from his rebuttal.

-- David L (bumpkin@dnet.net), July 24, 2000.

Prior to my initial post, I'd only skimmed his book. Now, I'm reading it. My degree of disagreement is very intense -- so far, at least. But the book is absolutely wonderful reading. Y'all gotta read it; even critics call it brilliant. And it's not overly long or technical; (about 200 pages).

But look at this (and there is a comment on the back cover itself that hints at what I'm coming to here) --

On page 170, he says,

"We may, to be more precise, have to relenquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth."

Now this is wild. He says, "...to be more precise..." In other words, he thinks HE's getting closer to the truth with his own statement, and in fact with his whole theory (really a paradigm itself), but his own theory says this can't happen!

In any case, since his whole theory would qualify as just another paradigm, his conclusion should be akin to a Dennis Miller quote:

"But, hey -- that's just MY opinion; I could be wrong."

I hope to be back with more on his theory as I get further into the book.

-- eve (eve_rebekah@yahoo.com), July 25, 2000.

With respect to my last post, actually it might be more accurate to infer his conclusion as follows (although I'm still in the process of trying to get a handle on the whole thing):

"But, hey -- I might be 'correct' in a limited sense for the time being; but the whole thing could be replaced tomorrow with something 'better', yet no closer to the truth."

(Sorry, I think I'd gotten a little carried away with the comic relief, re the Dennis Miller reference.)

-- eve (eve_rebekah@yahoo.com), July 25, 2000.

Hi eve,
Good catch. It gives new meaning to the phrase, "hoist with one's own petard."

-- David L (bumpkin@dnet.net), July 25, 2000.

The contradiction here is even more profound than you describe. Most of the world, and certainly Kuhn's part, has changed drastically since his birth, almost invariably for the better in material ways. He's healthier, lives longer, has more leisure time to write, more affluence, more lifestyle options, more time and energy to contemplate spiritual things, and he can get his message to far more people far more quickly than ever before.

And his message is that we're basically treading water and getting nowhere!

-- Flint (flintc@mindspring.com), July 25, 2000.

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